razor tight security at times square. on the streets of the at the starting line of today's marathon. >> with it comes security. i'm pretty sure they'll be nice and tight. >> reporter: millions cheering from the sidelines. >> we're here for the moral support. >> reporter: many on edge after last week's terror attack that left eight dead and 12 injured. >> there's a lot going on and you have to be worried and nervous. >> reporter: among the crowds there are also those that have seen terrorism firsthand. some on 9/11. >> i was in lower manhattan when the tower fell. >> reporter: others at the boston marathon bombing. >> right after boston our attitude was we're running next year regardless. >> reporter: officials say the more visible the security, the better. >> we have people here from all over the globe. my message is we will keep them safe. >> trains, tunnels, bridges, airports, you'll see an increased presence of law enforcement at all those locations. >> reporter: but despite concerns many people have, today's crowds u